Method of refining metals



Jan. 2, 1962 K. J. KORPI ETAL METHOD OF' REFINING METALS Filed Oct. 16, 1958 ELECWWC Fl//VCE A ENT METHOD F FHNEJG METALS Karl J. Korpi, Pasadena, alif., and Raymond C. .lohnson, Qrwigshurg, Pa., assignors to The Lummus Company, New York, NY., a corporation oi Delaware Filed Oct. 16, 1958, Ser. No. 757,632 9 (Claims. (Cl. '7S- $42.31)

This invention relates to the production of high melting point metallic elements and has for an object the provision of an improved method or process for producing high-purity refractory metals. More particularly, the invention contemplates the provision of an improved method or process for producing high-purity, high melting point metallic elements, including titanium, Zirconium, hafnium, vanadium and uranium, by the disproportionation of lower iodides of such elements. This application is a continuation-impart of our copending application Serial Number 575,792, tiled April 3, 1956, now abandoned, and entitled Method of Relining Metals.

Titanium, zirconium, hafnium, vanadium and uranium have become important commercial materials in view of the unusual properties which they exhibit. At present, there are several Ways of recovering such metals all of which are complicated and expensive. For instance, the

procedures now used for the manufacture of titanium are the following:

(l) Reduction of titanium tetrachloride or other titanium tetrahalide with either sodium or magnesium with subsequent elimination of the sodium or magnesium halide which is formed by washing or distillation.

(2 Reduction of titanium oxide with calcium hydride at elevated temperature. This procedure has not been too successful since the product is always heavily contaminated with oxygen.

(3) Thermal dissociation of a titanium tetrahalide on a hot filament under vacuum.

(4) Electrolytic recovery from fused salts.

At the present time, the most widely used commercial method is the reduction of titanium tetrachloride with magnesium or sodium followed by subsequent distillation of the magnesium chloride or sodium chloride byproduct in a vacuum. This process, popularly referred to as the Kroll process, is inherently expensive since it produces a titanium halide from a titanous ore and then reduces the halide with another substantially pure metal. In such a process, the necessary expense of the pure secondary metal establishes a very high minimum cost. Also the titanium is formed as a metallic sponge which necessitates further processing to obtain the metal in a useable form. p

As indicated, titanium, as well as the other aforementioned metals, have many unusual physical and chemical properties. In order to be workable and generally useful, these metals have to be supplied in an extraordinarily pure form. Small percentages of oxygen, nitrogen, hydrocarbon or carbon embrittle the metal markedly so that it cannot be handled by conventional metal working procedures.v Under these conditions,` great care is taken to `eliminate these undesirable elements from being present whilethe metal is being formed. While `the abo-ve noted processes are illustrative of titanium recovery, they are in principle applicable to other metal recovery in pure elemental form. These processes usually involve the recovery of crystalline metals in the foim ofl extremely small particles or a sponge form of metal. The small particles are inherently unstable and even pyrophoiic, readily oxidizing in the presence of air or Water, and even react with nitrogen from the air to form nitn'des of the metal.

.Other diiliculties with the treatment and recovery of these metals result from their high melting point. The

l?, property of titanium, in the molten state, of acting as a nearly universal solvent presents a major problem in handling the metal in such a state. Almost all of the impurities tolerable in other materials reduce the ductility of the high melting point metals to the degree of being unworkable.

To illustrate our process of producing high purity, high melting point, metallic elements we have hereinafter described our invention with regard to the treatment and recovery of titanium.

In accordance with the present invention, the metal titanium is produced as a relatively high purity product of the little known reaction of titanium monoxide with the titanium halides. Although the reactions of decomposition of sub-halides to metal and higher halides has been known, the possibilities of combined titanium halide reactions have not been appreciated. Through our invention pure ductile titanium is produced in plate or ingot form, rather than in oxidizable crystals or sponge form and at a cost substantially below that of present day methods. Further, our invention provides a relatively low temperature process which can operate at substantially atmospheric pressure with a minimum of heat input and Without the need for hydrogen or other costly reducing materials such as sodium or magnesium. Other objects and advantages of our invention will appear from the following description of one formof embodiment taken in connection with the attached drawing which is a simplified ilo-w diagram of the reaction according to the invention.

In view of the various metals recoverable and variations of equipment which may be used to carr] out our process, the flow diagram is to be considered of genorally informative nature and illustrative of process steps rather than a limitation as to a specific metal or type of apparatus. v

Accordingly, in our method, titanium bearing ores Vsuch as rutile, ilmenite and titanite or titanium dioxide-bearing slag obtained as a result of the smelting of titaniferous iron ore, are charged to pulverizer l0. These ores or slag, even in their purest state, contain iron, silicon and aluminum as regular impurities. Alkaline earth metals, such as calcium, are likewise commonly found in various titania rich ores. We reduce the titanium dioxide of such ores With powdered carbon supplied to pulverizer i2 and produce titanium contaminated with lower oxides including TigOg, 'H203 and TiO, and titanium carbide in furnace 14. The reducing agent fed to pulverizer 12 may be derived from any known carbon source; however, in order to limit contamination of the lower oxides of titanium, we prefer to employ petroleum coke or charcoal. The carbon in the mixture serves primarily to remove the oxygen from the titanium dioxide in the form of carbon monoxide and carbon dioxide, thereby reducing the titanium dioxide to titanium.- Some of the carbon may react with the titanium dioxide to form titanium carbide and carbon monoxide and carbon dioxide. To prepare titanium in furnace 14, we have used a mixture of parts by weight of crushed rutile and27 parts by weight of crushed petroleum coke, consolidated hy pressure to a dense solid. Analysis of the rutile and petroleum coke used by us indicated the following. t

Percent The Afurnace i4 may be an electric resistance furnace or it may be of any typical arc, cupola or uidized design. In the lfurnace, the titanium dioxide is reduced by carbon by a series of step-wise reactions to produce lower oxides of titanium, elemental titanium, and titanium carbide in accordance with the following chemical equations:

(l) TiOz-l-CeTiO-kCO' (becomes favorable about 900-l000 C.) (2) TiOg-l-ZC-Ti-l-ZCO (becomes favorable about 150l600 C.) (3) TiO2-{-CO- TiO-l-CO2 (favorable above 100 C.) (4) TiO2-l3C- TiC-l-2CO (becomes favorable about 9001000 C.)

favorable `about 2000-2l00 C.)

A mixed product of TiO and TiC may be obtained in furnace i4 by carrying out the reaction at a temperature of 900-1 100 C. ln presence of excess carbon, titanium carbide will be the favored product near 1000 C. at atmospheric pressure according to reaction 3. However, it is desired to make the maximum of metal and a minimum of carbide and lower oxides, hence the furnace must be heated to from 150G-2100 C. with the proper carbon ratio to promote reactions 2 and 5. The carbon monoxide `and dioxide formed during reduction is driven off under suitable conditions through line 16.

Products of the furnace other than carbon monoxide and carbon dioxide are cooled to about 700 C. and are in the form of a fused agglomerato containing titanium, titanium carbide and titanium monoxide plus impurities such as small amounts of iron, chromium, vanadium and silicon. This material is ground or pulverized in pulverizer i8 for further handling.

The pulverized titanium-titanium monoxide mixture is then charged to reactor 20, which is operated under conditions to exclude oxygen, nitrogen and moisture. This reactor is preferably maintained at a temperature above about 1025 C. and at substantially atmospheric pressure. Under the conditions of elevated temperature and controlled atmosphere, the pulverized crude titanium mixture introduced to the reactor is subjected to the action of a higher metal iodide vapor (MXh) entering through line 22 so that anY exotherrnic reaction results.v The reaction in reactor is so exothermic in nature that only enough heat to start up is needed from an external source. The temperature within the reactor is controlled by the amount of halide vapor input through line 22.

We have found that any of the halides which readily combine with titanium may be used to form the halide vapor entering reactor 20 through line 22; Principally we have formed metallic titanium according to our process using iodine, as the combined halogen presen-t in the higher metallic halides (MXh) and the lower metallic halide' (Mxl). n

For the purpose of general explanation, the metal and halide portions of all compounds illustrated in the drawing are represented by the symbols M and X, respectively with h and "'l designating the higher and lower halide form, respectively. Y

The vapor in line 22 is principally a higher halide of titanium (MXh) but in Ysorrie cases may include equilibrium amounts of lower halides. The vaporous higher khalide enters reactor 20 through the bottom and passes upwardly through the pulverized titanium mixture and upon reactiontherewith forms a vaporous mixture of Y* lower and higher halides (MXL` and MXh) which is free of carbon and impurities such as titanium monoxide,

4 titanium dioxide and titanium carbide and which is removed from the top of reactor 20 through line 24. The maximum temperature which may be maintained in the reactor 20 must be below the decomposition temperature of the lower halide (MX1) The titanium higher halides function somewhat in the manner of carriers in accordance with specific reactions illustrated by the following equations:

The titanium oxides and carbide present in the reactor charge that do not react with the higher halides under the aforementioned conditions, remain behind in the reactor as impurities. VThe carbon may be removed through line 26 and returned to pulverizer 12.

The impurities of line 2%, comprising mainly titanium carbide and titanium monoxide, can be introduced into an auxiliary reactor (not shown) for further reaction to produce lower halides of titanium according to the following equations:

Both of these reactionsrare favorable at temperatures below about 500 C.; hence such auxiliary reactor should be operated at about 400 C. while the tetrahalide vapor is introduced. This reactor should be operated batchwise so that after charging and reacting the solid titanium carbide and titanium monoxide with the tetrahalide vapor, such reactor is then heated to the melting point of the dihalide of titanium. Under these conditions, the trihalide disproportionates to dihalide and tetrahalide and the liquid dihalide may thereafter flow to jointhe llow of liquid dihalide in line 24. The tetrahalide vapors may remain. in the auxiliary reactor to react with a fresh charge of titanium carbide and titanium monoxide at the lower temperatures with additional tetrahalide added as required.

The vaporous lower and higher halide mixture (MXl and MXh) removed from reactor 20 through line 24 is then charged to a second reactor 30 which contains a. plurality of electric heating elements generally indicated at 32. Each heating element is enclosed in a metal (M) sheath 34 and is maintained at a temperature of from 800 C. to l500 C. The vaporous lower halide is condensed to form a liquid pool of the lower halide Within reactor 30 which is maintained by the sheathed heaters to an average temperature of between 625 C. and 1025 C. and in this temperature range, the lower metallicv halide is thermally disproportionated to form the metal, which deposits on the sheaths or collectors in-a high state of purity, and to higher metallic halides (MXh).

The decomposition of titanium dihalide to yield metallic titanium is according to the followingeguation:

v 'r1 Tixg (liquid) (solid) (EBS) Any titaniumV trihalide which may be present is generally unstable and dissociates into titaniumdihalide and The tetrahalide and some vof the titanium tetrahalide. unreacted dihalide formed during the thermal disproportionation in reactor v30 is in ar gaseousstate andis removed through line 36 and pumped by pump 38 to con used for reacting with titanium proceeds in continuous Y 'Y circulation between reactors 20 and 30. Only a small amount of the higher halide (MXh) is necessary' as i' Vmake-up since the halide circuit is substantially closed withV only small amounts of halide loss through the f ormation of volatile halides of the metallic impurities in the raw material.

Within the reactor 30 there is a continuous deposition and growth of metal on the heater sheaths 34 whereby they obtain the form of an ingot. Periodically the sheaths are removed and form the pure metal product, after which a new sheath is placed over the heating element and returned to the liquid pool of lower metallic halide.

Around each heater sheath is a refractory thermal barrier 46 which acts to substantially shield the liquid pool of lower halide from the higher temperature of the heater while at the same time directs the liquid halide in recirculating flow past the sheath for disproportionation.

In some instances the heating elements may also be maintained in the vapor phase over the liquid in reactor 3) as for example where it is found that the particular lower halide used disproportionates more rapidly as a vapor.

To illustrate a preferred embodiment of our process, operating conditions for the deposition of high purity titanium, are set forth in the following example.

Example Vaporous titanium tetraiodide (TiI4) at a 'temperature in the neighborhood of 380 C. reacts rapidly with 'crushed slag (comprised of lower titanium oxides7 titanium, titanium carbide and small amounts of impurities) in a bed maintained at a temperature in the neighborhood of ll50 C. at atmospheric pressure to form a vaporous titanium diiodide and titanium tetraiodide mixture of about .29 mole 'H14 and .71 mole Tilz per mole of such mixture. The diiodide is then condensed to form a liquid pool at a point-removed from the slag bed. The liquid titanium diiodide, maintained at a temperature in the neighborhood of 750 C. at atmospheric pressure, disproportionates to titanium and titanium tetraiodide vapor in the presence of a heated titanium sheath (950 C.) immersed within the pool. The titanium tetraiodide vapor is continuously withdrawn from the space above the pool and recirculated for use as the slag halogenating media. Analysis of the titanium coating on the titanium sheath shows only slight porosity and the presence of only trace impurities.

Having nowV described' our `invention with regard to the production of elemental titanium, zirconium, hafnium, vanadium and uranium and having given an example of a preferred embodiment of our process using titanium as the exempliiiedproduct, we desire a broad interpretation of the invention Within the scope of the disclosure herein and the following claims.

We claim:

'1. The method of producing a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium and uranium by the disproportionation of a lower iodide of the metal to form the metal and a higher iodide of the metal which comprises: halogenating a crude mixture of said metal with a higher iodide of said metal to form a lower iodide of said metal; edecting said halogenation in a irst reaction zone and at a temperature above the boiling point of said lower iodide of the metal and above the boiling point of said higher iodide of the metal thereby to form said lower iodide of said metal in said zone; withdrawing said lower iodide vas a vapor from said iirst reaction zone; condensing said vaporous lower iodide and effecting the disproportionation of said condensed lower iodide in a second reaction zone in the presence of a heated body of said metal by forming a liquid pool consisting primarily of said lower iodide around said body while maintaining the liquid pool at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated to a temperature suliicient to maintain said pool temperature; depositing a substantially solid layer of disproportionated metal on said body; and recirculating the higher iodide formed during disproportionation to said rst reaction zone to provide the higher iodide utilized for said halogenation.

2. The method of producing a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium and uranium by the disproportionation of a lower iodide of the metal to form the metal and a higher iodide of the metal which comprises: halogeuating a crude mixture of said metal with a higher iodide of said metal to form a lower iodide of said metal; eecting said halogenation in a rst reaction zone and at a temperature above the boiling point of said lower iodide of the metal and above the boiling point of said higher iodide of the metal thereby to vform said lower iodide of said metal in said zone; withdrawing said lower iodide as a Vapor from said first reaction zone; condensing said vaporous lower'iodide and effecting the disproportionation of said condensed lower iodide in a second reaction zone in the presence of a heated body of said metal by forming a iquid pool consisting primarily of said lower iodide around said body while maintaining the liquid pool at a temperature above the melting point and below the boiling point of said lower iodide by thermally induced circulation of said liquid up through a shield surrounding said body and over said body, said body being heated to a temperature suticient to maintain said pool temperature; depositing substantially solid layer of disproportioned metal on said body; and recirculating the higher iodide formed during disproportionation to said first reaction zone to provide the higher iodide utilized Y for said halogenation.

3. The method of producing titanium by the disproportionation of a lower iodide of titanium to form titaniumand a higher iodide of titanium which comprises; halogenating a crude mixture of titanium with a higher iodide of titanium to form a lower iodide of titanium; effecting said halogenation in a iirst reaction zone and at a temperature above the boiling point of said iodide of titanium and above the boiling point of said higher iodide of titanium thereby to form said lower iodide of titanium in said zone; withdrawing said lower iodide as a vapor from said tirst reaction zone; condensing said vaporous lower iodide and effecting the disproportionation of said condensed lower iodide in a second reaction zone in the presence of a heated body of titanium by forming a liquid pool consisting primarily of said lower iodide around said body while maintaining the liquid pool at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated to a temperature suiiicient to maintain said pool temperature; depositing substantially solid layer of disproportionated titanium on said body; and recirculating the higher iodide formed during disproportionation to said rst reaction zone to provide the higher iodide utilized for said halogenation. 4. The method of producing zirconium by the disproportionation of a lower iodide of zirconium to form zirconium and a higher iodide of zirconium which comprises: halogenating a crude mixture of zirconium with a higher iodide of zirconium to form a lower iodide of zirconium; effecting said halogenation in a iirst reaction zone and at a temperature above the boiling point of said p lower iodide of zirconium and above the boiling point of said higher iodide ofv zirconium thereby to form said lower iodide of zirconium in said zone; withdrawing said lower iodide as a vapor from said iirst reaction zone; condensing said vaporous lower iodide and etecting the dispro- `portionation of said condensed lower iodide in a second reaction zone in the presence of a heated body of zirconium by forming a liquid pool consisting primarily of said lower iodide around said body while maintaining the liquid pool at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated to a temperature sufficient to maintain said pool temperature; depositing a substantially solid layer of disproportionated zirconium on said body; and recirculating the higher iodide formed during disproportionation to said first reaction zone to provide the higher iodide utilized for said halogenation.

5. The method of producing hafnium by the disproportionation of a lower iodide of hafnium to form hafnium and a higher iodide of hafnium which comprises: halogenating a crude mixture of hafnium with a higher iodide of hafnium to form a lower iodide of hafnium; effecting said halogenation in a first reaction zone and at a temperature above the boiling point of said lower iodide of hafnium and above the boiling point of said higher iodide of hafnium thereby to form said lower iodide of hafnium in said zone; withdrawing said lower iodide as a vapor from said first reaction zone; condensing said vaporous lower'iodideV Yand effecting the'disproportionation'of said condensed lower iodide in a second reaction zone in the presence of a heated body of hafnium by forming a'liquid pool consisting primarily of said lower iodide around said body while maintaining the liquid pool at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated to a temperature sufficient to maintain said pool temperature; depositing a substantially solid layer of disproportionated hafnium on said body; and recirculating the higher iodide formed during disproportionation to said first reaction zone to provide the higher iodide utilized for said halogenation.

6. The method of producing vanadium by the disproportionation of a lower iodide of vanadium to form vanadium and a higher iodide of vanadium which comprises: halogenating a crude mixture of vanadium with a higher iodide of vanadium to form a lower iodide of vanadium; electing said halogenation in a iirst reaction zone and at a temperature above the boiling point of said lower iodide of vanadium and above the boiling point of said higher iodide ofvanadium thereby to form said lower iodide of vanadium in said zone; withdrawing said lower iodide as a Vapor from said first reaction zone; condensing vsaid vaporous lower iodide and effecting the disproportionation of said condensed lower iodide in a second reaction zone in the presence of a heated body of vanadium by forming a liquid pool 'consisting primarily of said .lower iodide around said .body while maintaining the liquid pool at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated to a temperature sufficient to maintain said pool temperature; depositing a substantially solid layer of disproportionated vanadium on said body; and recirculating the Ahigher iodide formed Vduring disproportionation to said irst lreaction zone to provide the higher iodide utilized for said halogenation.

7. The method of producing uranium by the disproportionation of a lower iodide of uranium to form uranium and a higher iodide of uranium which comprises:

halogenating a crude mixture of uranium with a higher iodide of uranium to form a lower iodide of uranium; ef-

fecting said halogenation in a first reaction zone and lat a temperature above the boiling point of said lower iodide of uranium and above the boiling point of said higher iodide of uranium thereby to form said lower iodide of uranium in said zone; withdrawing said lower iodide as a vapor from said rst reaction; condensing said vaporous lower iodide and effecting the dsproportionation of said condensed lower iodidein a second reaction zone in the presence of a heated body of uranium by forming a liquid pool consisting primarily of said lower iodide around said body while maintaining the liquid at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated to a temperature sufficient to maintain said pool temperature; depositing a substantially solid layer of disproportionatedrurallum 011 said body; and reciroulating the higher iodide formed during disproportionation to said first reaction zone to provide the higher iodide utilized for said halogenation.

8. The method of producing a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium and uranium by the disproportionation of a lower iodide of the metal to form the metal and a higher iodide of the metal Which comprises: halogenating in a first reaction zone a crude mixture of said metal with a higher iodide of said metal to form a lower iodide of said metal and solid impurities including oxides and carbides of said metal; withdrawing said lower iodide las a Vapor from said first reaction zone; condensing said vaporous lower iodide of said metal; separately halogenating in a second reaction zone said solid impurities with a lsecond portion of said higher iodide of said metal to form a second source of the lower iodide of said metal; withdrawing said second portion of said lower iodide as a liquid Vfrom said second reaction zone; effecting in a third reaction zone the disf proportionation of the combined poitions of the liquid lower iodide of said metal in plate form into said metal and the higher iodide of said metal; and recirculating -said higher iodide of said metal as said halogenating media.

9. The method of producing relatively pure metals as claimed in claim 8 wherein the crude mixture is halogenated at substantially atmospheric pressure vand at a temperature above the boiling point of said lower iodide of said metal and the impurities from said iirst halogenation are separately halogenated at substantially atmospheric pressure and at a temperature below the melting point'of said lower iodide ofsaid metal and above the boiling point of said higher iodide of said metal.

References Cited in the iile of this patent n UNITED STATES PATENTS K 2,670,270 Jordan Feb. 23, 1954 1 2,706,153 Glasser Apr, 12, 1955 2,785,973 Gross i. Mar. 19, 1957 2,89),952 Korpi et al. .s .lune 16, 1959 

1. THE METHOD OF PRODUCING A METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM ZIRCONIUM HAFNIUM, VANADIUM AND URANIUM BY THE DISPROPORTIONATION OF A LOWER IODIDE OF THE METAL TO FORM THE METAL AND A HIGHER IODIDE OF THE METAL WHICH COMPRISES: HALOGENATING A CRUDE MIXTURE OF SAID METAL WITH A HIGHER IODIDE OF SAID METAL TO FORM A LOWER IODIDE OF SAID METAL; EFFECTING SAID HALOGENATION IN A FIRST REACTION ZONE AND AT A TEMPERATURE ABOVE THE BOILING POINT OF SAID LOWER IODIDE OF THE METAL AND ABOVE THE BOILING POINT OF SAID HIGHER IODIDE OF THE METAL THEREBY TO FORM SAID LOWER IODIDE OF SAID METAL IN SAID ZONE; WITHDRAWING SAID LOWER IODIDE AS A VAPOR FROM SAID FIRST REACTION ZONE; CONDENSING SAID VAPOROUS LOWER IODIDE AND EFFECTING THE DISPROPORTIONATION OF SAID CONDENSED LOWER IODIDE IN A SECOND REACTION ZONE IN THE PRESENCE OF A HEATED BODY OF SAID METAL BY FORM ING A LIQUID POOL CONSISTING PRIMARILY OF SAID LOWER IODIDE AROUND SAID BODY WHILE MAINTAINING THE LIQUID POOL AT A TEMPERATURE ABOVE THE MELTING POINT AND BELOW THE BOILING POINT OF SAID LOWER IODIDE SAID BODY BEING HEATED TO A TEMPERATURE SUFFICIENT TO MAINTAIN SAID POOL TEMPERATURE; DEPOSITING A SUBSTANTIALLY SOLID LAYER OF DISPROPORTIONATED METAL ON SAID BODY; AND RECIRCULATING THE HIGHER IODIDE FORMED DURING DISPROPORTIONATION TO SAID FIRST REACTION ZONE TO PROVIDE THE HIGHER IODIDE UTILIZED FOR SAID HALOGENATION. 